# FBI employees 2003
# DEA employees 2003
ATF is a little harder to come to because they are an arm of the US Treasury.
Don't forget the Secret Service.
Fish and wildlife might be of interest also. I wasn't able to find their numbers on their website.

As far as having a more aggressive police force because of all the veterans coming back, I'm not to sure about that, but you could probably check the number of police brutality cases in years following conflicts. You can find that info at the DOJ website.